(a) Field of the Invention
The present invention relates to a pixel circuit and a display device.
(b) Description of the Related Art
In recent years, various display devices, such as organic EL displays (organic Electroluminescence displays, also called as OLED displays (Organic Light Emitting Diode displays)), FEDs (Field Emission Displays), PDPs (Plasma Display Panels), and the like, have been developed as devices to replace CTR displays (Cathode Ray Tube displays).
Amongst the various display devices mentioned above, the organic EL displays are self-luminescence type display devices that use an electroluminescence phenomenon.
They have drawn particular attention of people as devices for the next generation, because they are superior to display devices in their moving image characteristics, viewing angle characteristics, color reproducibility, etc.
The electroluminescence phenomenon is a phenomenon in which the state of an electron of a material (an organic EL element) changes from the ground state to the excited state so as to return from the excited state, which is unstable, to the ground state, which is stable, whereby the difference of energy is emitted in the form of light.
Moreover, high picture quality technologies for a display device having an organic EL element as a light emitting element have been developed.
An example of the technology for achieving high picture quality by compensating for variations in the characteristics of a driving transistor of each pixel may include the technology of Patent Document 1.
In the case of a display panel (e.g., active matrix display panel) of a display device having an organic EL element (hereinafter, simply referred to as a display device) which is formed of, for example, low-temperature polysilicon (LTPS), variations may occur in the characteristics of a thin film transistor (hereinafter, may be simply referred to as a transistor) of each pixel.
The light emission luminance of the organic EL element changes with the amount of current flowing through the organic EL element.
Accordingly, when there occur variations in the characteristics of a transistor of each pixel, the amount of current flowing through the organic EL element of each pixel changes, and as a result non-uniformity appears in a displayed image.
In this regard, it is preferable to compensate for variations in the characteristics of a transistor of each pixel in order to achieve high picture quality by preventing deterioration of display quality.
Examples of methods for compensating for variations in the characteristics of a transistor may include a method (internal correction) in which variations in the characteristics of a transistor are compensated for inside a pixel and a method (external correction) in which variations in the characteristics of a transistor are compensated for by generating correction data in a circuit outside a pixel.
For example, internal correction is mainly used for a display device (so-called small or medium sized display panel) employed in portable devices such as cell phones, smartphones, etc, due to the demand for cost reduction or circuit area reduction.
In the case of internal correction, as exemplified in a conventional pixel of Patent Document 1, a plurality of transistors and a capacitor element (capacitor) need to be formed within a pixel (hereinafter, a circuit constituting a pixel will be referred to as a pixel circuit).
However, there is the possibility that an increase in the number of transistors constituting a pixel circuit may cause, for example, a reduction in the aperture ratio of the display panel.
Moreover, assuming that display panels are upscaling from HD (High Definition) resolution, 4K resolution, 8K resolution, and beyond, an increase in the number of transistors constituting a pixel circuit may realize a high-precision display panel, but at the same time cause a failure.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.